@unpublished{backwards,
  title = "Be Kind, Rewind: A Modest Proposal about Traversal",
  author = "Jeremy Gibbons and Richard Bird",
  year = "2012",
  month = "May",
  note = "Submitted for publication (but rejected)",
  url = "http://www.comlab.ox.ac.uk/jeremy.gibbons/publications/backwards.pdf",
}